Positive type photosensitive epoxy resin composition and printed circuit board using the same

ABSTRACT

A positive type, photosensitive epoxy resin composition comprising (a) an epoxy resin having two or more epoxy groups in one molecule, (b) a modified phenolic resin having a triazine ring, (c) a latent basic curing agent and (d) a photosensitive acid generator; and a preferably multilayered printed circuit board of buildup mode using said composition as an insulating layer.

The present invention relates to a positive type photosensitive epoxyresin composition successfully usable as an insulating layer in aprinted circuit board, for instance as a solder resist layer or,particularly as an interlaminar insulating layer in a multilayeredprinted circuit board of buildup mode in which conductor circuit layersand interlaminar insulating layers are piled up alternately; and amethod for producing a multilayered printed circuit board of buildupmode using said epoxy resin composition.

BACKGROUND OF THE INVENTION

The desire of the time for the size and enhancing the performance ofelectronic devices has promoted various rapid progresses in the field ofmounting substrate, such as making thinner the wiring of multilayeredprinted circuit board in which substrate circuits are formed into amultilayered structure, increasing the number of layers and enhancingthe density of wiring. As its result, prior multilayered wiring boardsin which the wiring layers are connected by through-holes have becomeincapable of coping with the desire for enhancing the wiring densitybecause of the large area occupied by through-holes. For such a reason,multilayered circuit board of buildup mode is actively studied in therecent years. In a multilayered printed circuit board of buildup mode,the wiring layers are connected one another through minute holes called“via holes”.

As the interlaminar insulating layer thereof, epoxy resin compositionsare used because of excellent electrical properties and adhesiveproperties of the compositions and excellent mechanical properties ofthe cured products thereof.

In addition, an interlaminar insulating layer is required to beflame-retarded from the viewpoint of safety, as typified by glassfiber-reinforced epoxy printed circuit boards, and they areflame-retarded by the use of halides (an example thereof is thebrominated epoxy resin) or antimony compounds. In the recent years,however, the official regulation on the materials using halides such asbromides and the like and antimony compounds is becoming severer. Inview of such a state of things, thermosetting interlaminar insulatinglayers using a triazine ring-containing epoxy resin as a curing agentfor epoxy resin have been proposed (JP-A 11-87927, 11-1547, and11-343398).

A buildup multilayered printed circuit board of photo-via mode using aphotosensitive resin as interlaminar insulating layers on which viaholes are formed by the photolithographic method has also been proposed.A buildup multilayered printed circuit board of photo-via type candecrease the diameter of via-holes, so that the area occupied bythrough-holes can be lessened to a great extent and, at the same time,many via-holes can be formed at once. Examples thereof include thenegative type photosensitive resin compositions constituted of epoxyacrylate and epoxy resin (JP-A 9-40751, 10-36682, 10-173336); thenegative type photosensitive resin compositions which are cured by theuse of epoxy resin, novolac type epoxy resin and acrylate (JP-A11-30855); the negative type photosensitive resin compositions in whichan epoxy resin and a resol type phenolic resin are cured with a cationicphoto-initiator (JP-A 5-136575); and the negative type photosensitiveresin compositions composed mainly of a chalcone-containingbisphenol-epichlorohydrin type epoxy resin (JP-A 8-236945).

The above-mentioned interlaminar insulating layer using a triazinering-containing phenolic compound as a curing agent for epoxy resin canachieve flame-retardation without use of brominated epoxy resin.However, this type of compositions are thermosetting, so that via-holescan be formed only by heat-curing the composition and thereafter formingthe holes one by one by means of carbon dioxide laser. It takes a longperiod of time to produce a printed circuit board having a number ofvia-holes by such a method.

Further, prior epoxy resin compositions having photosensitivity havebeen difficult to flame-retard without use of brominated epoxy resin.Further, the above-mentioned photosensitive resin compositions are ofnegative type in which an area exposed to active energy beam cures andthe unexposed area is removed by the process of development.Accordingly, the active energy beam is absorbed into resin and diffusedat the time of exposure and the extent of cure differs with depth ofinterlaminar layer, due to which the via holes formed by developmentassume an inversely tapered shape. This can deteriorate the throwingpower in the subsequent copper-plating step and thereby cause adefective connection.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a positive type photosensitive epoxy resin composition whichmakes it possible to realize flame-retardation without use of brominatedepoxy resin and, at the same time, to form regularly tapered via-holesby a lithographic method in which the exposed area is removed by theprocedure of development.

In order to achieve the object mentioned above, the present inventionprovides a flame-retardant positive type photosensitive epoxy resincomposition comprising (a) an epoxy resin having two or more epoxygroups in one molecule, (b) a modified phenolic resin having a triazinering, (c) a basic curing agent and (d) a photosensitive acid generatoras essential ingredients from which an area exposed to active energybeam can be eliminated by a procedure of development; a method forforming an insulating layer using said epoxy resin composition and aprinted circuit layer board comprising such an insulating layer, inparticular a multilayered printed circuit board of buildup modecomprising at least one of said insulating layers as interlaminar layer.

DETAILED DESCRIPTION OF THE INVENTION

The ingredients constituting the positive type photosensitive epoxyresin composition of the present invention will be explained below.

The epoxy resin used in the present invention can be obtained by a knownprocess which comprises reacting a divalent or polyvalent, mononuclearor polynuclear phenol compound with epichlorohydrin in the presence ofan alkaline catalyst.

As the divalent phenol compound, for example, the following can bereferred to: resorcinol, hydroquinone, pyrocatechin,1,4-dihydroxy-2,5-tert-butyl-benzene, 1,4-dihydroxynaphthalene,4,4′-dihydroxy-biphenyl, 4,4′-dihydroxy-3,3′, 5,5′-tetramethylbiphenyl,Bisphenol F, 1,1-bis(4-hydroxyphenyl)ethane, Bisphenol A,bis(4-hydroxyphenyl)-methylphenyl-methane,bis(4-hyroxyphenyl)-tolyl-methane, 1,1-bis(4-hydroxyphenyl)cyclohexane,bis(4-hydroxyphenyl)dicyclopentane,bis(4-hydroxy-3,5-dimethylphenyl)dicyclopentane,4-[1-[4-(4-hydroxy-3methylphenyl)-4-methylcyclohexyl]-1-methylethyl]-2-methylphenol,4,4′-(9H-fluoren-9-ylidene)bisphenol, 4,4′-dihydroxybenzophenone,bis(4-hydroxyphenyl) sulfone, bis(4-hydroxyphenyl) sulfide,bis(4-hydroxy-3,5-dimethylphenyl)methane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,4,4′-[1,3-phenylenebis(1-methylethylidene)]-2,2′,6,6′-bisphenol,4,4′-[1,4-phenylenebis(1-methylethylidene)]-2,2′,6,6′-bisphenol andbis(4-hydroxy-3,5-dimethylphenyl)methane.

As the trisphenols which belong to polyphenol compounds,4,4′,4″-methylidyne-trisphenol, 4,4′,4″-ethylidyne-trisphenol and4,4′-[1-4-[2(4-hydroxyphenyl)-2-propyl]phenyl]ethylidene]bisphenol canbe referred to.

As the tetrakisphenol which belong to polyphenol compounds,1,1,2,2-tetrakis(4-hydroxyphenyl)ethane can be referred to.

Novolacs which belong to polyvalent phenol compounds can be obtainedaccording to the known process which comprises reacting a bifunctionalor tri- or higher-functional, mononuclear or polynuclear phenol compoundis reacted, in the form of a single compound or a mixture of two or morecompounds, with an aldehyde such as formaldehyde, paraformaldehyde,trioxane, acetaldehyde, benzaldehyde or the like or with an unsaturatedalicyclic hydrocarbon such as dicyclopentadi ne, cyclic t rpene and thelike or with methoxydimethylbenzene in the presence of an acid catalyst.As said bifunctional or tri- or higher-functional, mononuclear orpolynuclear phenol compound, the following can be referred to: phenol,p-cresol, o-cresol, m-cresol, p-ethylphenol, p-propylphenol,p-tert-butylphenol, p-octylphenol, p-methoxyphenol, p-nonylphenol,1-naphthol, 2-naphthol, 3,5-xylenol, resorcinol, catechol, Bisphenol Aand Bisphenol F.

As epoxy resins other than the above, the following can be referred to:glycidylamines obtained by reacting epichlorohydrin with an amine havingat least two amino-hydrogen atoms and then dehydrochlorinating thereaction product, such as N,N-diglycidylaniline,N,N-tetraglycidyl-4,4′-diaminodiphenylmethane,N-diglycidyl-4-amino-phenyl glycidyl ether and the like; heterocyclicepoxy resins obtained by reacting a heterocyclic compound withepichlorohydrin, such as triglycidyl isocyanurate,5,5-dimethyl-N,N′-diglycidylhydantoin and the like; glycidyl esters ofpolybasic aromatic, aliphatic and alicyclic carboxylic acids, such asdiglycidyl terephthalate, diglycidyl adipate, diglycidylhexahydrophthalate, triglycidyl trimellitate, diglycidyl ester ofdimerized unsaturated fatty acid and the like; glycidylesters of(meth)acrylic acid and polyglycidylesters of (meth)acrylic acid polymersand copolymers, polyglycidyl ethers obtained by reacting a polyhydricalcohol-containing compound with epichlorohydrin under an alkalinecondition or in the presence of a phase-transfer catalyst and an alkalior by reacting a polyhydric alcohol-containing compound in the presenceof an acid catalyst and then treating the product with an alkali, suchas butane-1,4-diglycidyl ether, hexane-1,6-diglycidyl ether,polypropylene glycol diglycidyl ether, trimethylolpropane glycidylether, 2,2-(bis(4-hydroxycyclohexyl)propane diglycidyl ether, diglycidylether obtained by reacting Bisphenol A with propylene oxide and thenreacting the reaction product with epichlorohydrin, diglycidyl etherobtained by reacting Bisphenol A with butyl glycidyl ether and thenreacting the reaction product with epichlorohydrin, glycidyl ether ofpolybutadiene having a terminal hydroxyl group; and the like. Asexamples of the epoxy resins which are not glycidyl compound, thefollowing can be referred to: vinylcyclohexane diepoxide,dicyclopentadiene epoxide, alicyclic epoxy resins such as3-(3′,4′-epoxycyclohexyl)-8,9-epoxy-2,4-dioxaspiro[5.5]undecane,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate,bis(3,4-epoxycyclohexyl) adipate and the like, and epoxidizedpolybutadiene.

Further, epoxy resins having an oxazolidone ring in the molecule thereofwhich are described in WO90/15089 can be referred to. The use of anepoxy resin having an oxazolidone ring makes it possible to improve theheat resistance of interlaminar insulating layer. Preferable epoxyresins having an oxazolidone ring and an epoxy group are reactionproducts between an epoxy resin having an epoxy equival nt of 170–210g/mol such as Bisphenol A type epoxy resin, Bisphenol F type epoxy resinor 4,4′,4″-methylidyne trisphenyl glycidyl ether and the like and abifunctional isocyanate such as tolylene diisocyanate, hexamethylenediisocyanate, methylenediphenyl diisocyanate and the like.

Preferable epoxy resins are Bisphenol A type epoxy resin, Bisphenol Ftype epoxy resin, phenol novolac type epoxy resin, cresol novolac typeepoxy resin, and epoxy resin having an oxazolidone ring in the moleculethereof. Preferable Bisphenol A type epoxy resin and Bisphenol F typeepoxy resin have an epoxy equivalent of 175 to 3,000 g/mol. A furtherpreferable epoxy resin is Bisphenol A type epoxy resin having an epoxyequivalent of 400 to 1,000 g/mol and a softening point of 40° C. to 100°C. A preferable novolac type epoxy resin has an epoxy equivalent of 175to 230 g/mol, and a preferable oxozolidone ring-containing epoxy resinhas an epoxy equivalent of 230 to 500 g/mol and an oxazolidone ringequivalent of 400 to 1,300 g/mol, and a softening point of 50° C. to120° C. Preferably, these epoxy resins have a hydrolyzable chlorinecontent of 1,000 ppm or less.Preferably, these epoxy resins have analpha(?)-glycol content of 100 mol/kg or less.

These epoxy resins may be used either alone or in combination of severalspecies in accordance with the object of use. In the selection ofcombination of the epoxy resins, it is important to compound the epoxyresins so that the composition does not adhere to photomask at the timeof exposure, and it is desirable that softening point of the compositionis not higher than 100° C. so that the composition can be developed witha developing solution. When an epoxy resin having a softening pointhigher than 100° C. is used, it is possible to used in combinationtherewith a liquid (at normal temperature) Bisphenol A type epoxy resinhaving an epoxy equivalent of 175 to 210 g/mol in an amount of 2 to 15%by weight, for the purpose of realizing a desirable softening point.Preferably the softening point of the composition is not higher than 60°C.

As the modified phenolic resins having a triazine ring which can be usedin the present invention, polycondensates formed between a phenolcompound, a compound having a triazine ring and an aldehyde can bereferred to. As the phenol compound, phenol, p-cresol, o-cresol,m-cresol, p-ethylphenol, p-propylphenol, p-tert-butylphenol,p-octylphenol, p-methoxyphenol, p-nonylphenol, 1-naphthol, 2-naphthol,3,5-xylenol, resorcinol, catechol, Bisphenol A, Bisphenol F and the likecan be referred to, which may be used alone or in combination of two ormore. As the compound having a triazine ring, melamine and guanaminessuch as benzoguanamin , acetoguanamine and the like can b referred to,which may be used alone or in combination of two or more. As thealdehyde, formaldehyde, para-formaldehyde, trioxane, acetaldehyde,benzaldehyde and the like can be referred to.

Among the modified phenolic resins having a triazine ring, preferred arethose having a phenolic hydroxyl equivalent of 120 to 300 g/mol, asoftening point of 80° C. to 150° C. and a nitrogen content of 4 to 25%by weight, and further preferable are those having a phenolic hydroxylequivalent of 150 to 250 g/mol, a softening point of 90° C. to 140° C.and a nitrogen content of 15 to 25% by weight. The triazinering-containing modified phenolic resin is compounded with epoxy resinpreferably in such an amount that the quantity of phenolic hydroxylgroup of the triazine ring-containing modified phenolic resin comes to0.2 to 0.8 equivalent per equivalent of the epoxy group in the epoxyresin, and further preferably in such an amount that the quantity ofhydroxyl group of the triazine ring-containing modified phenolic resincomes to 0.2 to 0.5 equivalent per equivalent of the epoxy group in theepoxy resin.

Any latent basic curing agent for epoxy resins may be used for thepurposes of the instant invention, for instance tertiary amine curingagents, in particular N,N,N′,N′-tetramethyl-1,3-butane diamine,benzyldimethylamine, 2-dimethylamino-2-hydroxypropane,2-(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminoethyl)phenol,latent urea curing agents like, forinstance,2-chloro-4(N,N′-dimethylureido)-toluene,2-(N,N′-dimethylureido)phenol, 4-(N,N′-dimethylureido)-chlorobenzene,and latent imidazole curing agents like the following imidazolecompounds: 1-methylimidazole, 2-methylimidazole, 2-ethylimidazole,2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole,2-ethyl-4-methylimidazole, 1-methyl-2-ethylimidazole, 2-phenylimidazole,2-phenyl-4-ethylimidazole, 1-benzyl-2-phenylimidazole,1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole,1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole,1-cyanoethyl-2-phenylimidazo 2-phenyl-4,5-dihydroxymethylimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole,1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, and epoxyadducts formed between these imidazole compounds and epoxy resins.

As examples of the epoxy adduct, adduct between 2-methylimidazole andBisphenol A type epoxy resin, adduct between 2-ethyl-4-methylimidazoleand Bisphenol A type epoxy resin, adduct between 2-phenylimidazole andBisphenol A type epoxy resin, adduct between 2-methylimidazole andcresyl glycidyl ether, adduct between 2-phenylimidazole and cresylglycicyl ether, and the like can be referred to.

Said epoxy adduct contains at least one kind of imidazole compoundpreferably in an amount of 0.01 to 0.10 equivalent and furtherpreferably in an amount of 0.015 to 0.04 equivalent per equivalent ofthe epoxy group of epoxy resin. Imidazole compounds like those mentionedbeforehand are the preferred latent basic curing agents for the purposesof the invention. The term “latent” is used to clarify that only curingagents which do not render a hardening reaction possible at lowtemperatures are intended to be used for the instant invention. For usein accordance with the invention it is advantageous to use basic curingagents with which the hardening reaction only tajkes place at anelevated temperature, preferably above 80° C. and especially above 100°C.

As the photosensitive acid generator, those compounds which can beinfluenced by active energy beam can be used, and examples thereofinclude aryl diazonium salts;diaryliodonium salts such asdiphenyliodonium tetrafluoroborate and the like; triarylsulfonium saltssuch as triphenylsulfonium hexafluoroantimonate and the like; arylacyldialkylsulfonium salts; 1,2-quinonediazide calboxylic acid-4-estergroup; 1,2-quinonediazide sulfonic acid-4-ester group such as4-trihydroxybenzophenone-1,2-naphthoquinonediazide-4-sulfonic acidester,4-(2-ethylhexanoyl)resorcinol-1,2-naphthoquinonediazide-4-sulfonic acidester and the like and iron arene complex compounds. Among thesephotosensitive acid generators, preferable are iron arene complexcompounds represented by the following formula:[R¹(Fe^(II)R²)]⁺[X]⁻In this formula, R¹ represents π-arene and R² represents π-arene orπ-arene anion. R¹ preferably represents η⁶-cumene, η⁶-naphthalene,η⁶-benzene or η⁶-pyrene. R² preferably represents an anion ofη⁵-cyclopentadiene. X represents a non-nucleophilic anion. Preferableexamples of X include BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, SbF₆ ⁻, SbF₅OH⁻; sulfonatessuch as methylsulfonate, p-toluenesulfonate and the like;perfluoroalkylsulfonates such as trifluoromethylsulfonate,nonafluorobutylsulfonate and the like; acetates such as CH₃COO⁻ and thelike; perfluoroacetates such as CF₃COO⁻ and the like; halides such asF⁻, Cl⁻, Br⁻, I⁻ and the like; and pseudo-halides such as CN⁻, SCN⁻ andthe like. Further preferably, X represents a sulfonate, aperfluorosulfonate or PF₆ ⁻.

The composition contains at least one iron arene complex compoundpreferably in an amount of 0.2 to 1.4 equivalents and furth r preferablyin an amount of 0.4 to 0.95 equivalent per equivalent of the imidazolecompound.

The composition of the present invention can be divided into fluid A andfluid B with consideration of storage stability. The modes of thedivision are, for example, as follows: Fluid A=epoxy resin, FluidB=triazine ring-containing modified phenolic resin, imidazole compoundand photosensitive acid generator; Fluid A=epoxy resin andphotosensitive acid generator, Fluid B=triazine ring-containing modifiedphenolic resin and imidazole compound. Preferably the fluid A and fluidB are mixed together just before the coating process.

In order to improve the follow-up property of the composition of thepresent invention to the conductor circuit pattern formed on thesubstrate and the leveling property thereof, the composition of thepresent invention may be diluted with a solvent to adjust its viscosityto a desired value. Organic solvents usable for this purpose include,for example, ketones such as acetone, methyl ethyl ketone, methylisobutyl ketone, cyclohexanone and the like; aromatic hydrocarbons suchas toluene, xylene and the like; cellosolves such as cellosolve, butylcellosolve and the like; carbitols such as methyl carbitol, dimethylcarbitol, butyl carbitol and the like; carboxylic esters such as ethylacetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate,methoxypropyl acetate, carbitol acetate, butyl carbitol acetate,γ-butyrolactone and the like; alcohols such as butanol, methoxypropanoland the like; N-methyl-2-pyrrolidone, N,N-dimethylformamide, anddimethylacetamide. These solvents may be used alone or in the form of amixture of two or more. Preferably, the composition which has beendiluted with the solvent has a viscosity of 200 to 30,000 mPa•s.

If desired, the composition of the present invention may contain knownadditives in addition to the above. Examples of such additives includeinorganic fillers such as barium sulfate, barium titanate, siliconoxide, talc, calcium carbonate, ammonium phosphate, mica, magnesiumhydroxide, aluminum hydroxide and the like; organic fillers such assilicone powder, nylon powder, fluoride powder and the like; thixotropicagents such as Aerosil, Orben, benton, montmorillonite and the like;colorants such as Phthalocyanine Blue, Phthalocyanine Green, CrystalViolet, titanium oxide and the like; antifoaming agents of silicone typeand fluoride type; leveling agents such as silicone acryl and the like;silane coupling agents; adhesion improvers such as mercaptotetrazole andthe like; anticoagulants for fillers; and antioxidants. In order toprevent the occurrence of a reaction at an excessively early stage dueto unexpected irradiation, an ultraviolet absorber and/or a yellow- orred-colored organic dyes are added in small amounts. Some of thefillers, colorants and thixotropic agents are insoluble in organicsolvent, and they may be any of globular ones, needle-like ones andamorphous ones are all usable, and the surface thereof may be treatedwith silane coupler or not treated. Preferably, the mean particlediameter is 10 μm or less and the quantity of filler added is 35% byweight or less. In a case where the composition contains a small amountof additive having a mean particle diameter greater than 10 μm, suchgreat particles can advantageously be filtered off before the coatingprocess onto the inner layer substrate. Preferably, the additives usedfor regulating the interface such as antifoaming agent, leveling agentand adhesion improver are used in an amount of 0.02 to 2% by weight.

Further, if desired, a sensitizer may be added for the purpose ofenhancing photosensitivity. Examples of the sensitizer includeanthracenes such as 9,10-diethoxyanthracene, 9-methylanthracene and thelike; acetophenones such as acetophenone, dimethoxyphenyl-acetophenoneand the like; and thioxanthones such as 2-isopropylthioxanthone,diethylthioxanthone and the like.

For compounding the above-mentioned additives into the composition ofthe present invention, the mixture is preliminarily kneaded withplanetary mixer, homogenizer or the like and then the mixture is finelydispersed by means of triple roll mill, wet ball mill, wet beads mill orthe like.

Further, in order to improve tenacity of the positive typephotosensitive epoxy resin composition of the present invention, a knownthermoplastic resin or a rubbery component may be used. As saidthermoplastic resin, phenoxy resin, polytetrafluoroethylene,polyethylene terephthalate, polysulfone, polyphenylene sulfide,polyether sulfone, thermoplastic polyimide, polyphenylene ether,modified polyphenylene ether, polyethylene naphthalate, polyether etherketone, polyvinyl butyral resin and the like can be used. As saidrubbery component, polybutadiene rubber, acrylonitrile-butadiene rubber,carboxyl group-containing acrylonitrile-butadiene rubber, encapsulatedpolybutadiene rubber and the like can be used.

Further, if aqueous alkaline developabilty is desired, the epoxycomposition according to the invention can contain an additional binderwhich is soluble in aqueous alkaline solutions, for example a polyphenolor a mixture of polyphenols, i.e. a polymer having a specific content ofphenolic hydroxyl groups. The content should at least be sufficientlyhigh to ensure development, or at least a swelling, in the aqueousalkaline solution of developer. Suitable film-forming binders, solublein aqueous alkaline solutions include the following groups:

-   (i) novolaks formed from at least one phenol and at least one    aldehyde,-   (ii) homopolymers and copolymers of alkenylphenols and, in    particular,-   (iii) homopolymers and copolymers of N-hydroxyphenylmaleinimides.    Such binders are described in more detail in U.S. Pat. No.    5,124,233, the disclosure of which is considered as being    incorporated into the instant description.

It is as well possible to impart the instant epoxy compositions adevelopability in aqueous alkaline solutions by incorporating asufficient amount of additives of low molecular weight to the epoxycomposition which render the composition soluble or at least swellablein aqueous alkali, for instance monomeric phenolic compounds.

The compositions of the instant invention are useful for manufacturinginsulating layers in particular for use in printed circuit boardtechnology.

Accordingly the instant invention relates also to a method for formingan insulating layer characterized by coating a substrate with a positivetype photosensitive epoxy resin composition comprising (a) an epoxyresin having two or more epoxy groups in one molecule, (b) a modifiedphenolic resin having a triazine ring, (c) an imidazole compound and (d)a photosensitive acid generator, followed by a step of preliminarydrying at a temperature not higher than the temperature at which thesubsequent heat curing step (I) is to be carried out, a step ofimagewise irradiating the coating with an active energy beam, forinstance through a photomask, a heat curing step (I), a step ofdissolving and eliminating the exposed area, and an additional heatcuring step (II).

Furthermore the instant invention relates to a printed circuit boardcomprising an insulating layer prepared with the aid of a positive typephotosensitive epoxy resin composition as described above, in particularto a multilayered printed board of buildup mode which comprises at leastone interlaminar insulating layer prepared with the aid of said positivetype photosensitive epoxy resin composition

Next, the method for preparing such a multilayered printed circuit boardof buildup mode using the positive type photosensitive epoxy resincomposition of the present invention will be mentioned as an example ofusing the epoxy compositions of the instant invention. At first, apositive type photosensitive epoxy resin composition of the presentinvention which has been diluted with an organic solvent is coated ontoa single layer or multilayer type circuit substrate on which a patternhas previously been fabricated, up to a thickness not smaller than thethickness of conductor circuit, namely up to a thickness of 10–100 μm,under a yellow- or red-colored light. Thereafter, the coated matter ispreliminarily dried at 60° C. to 90° C. It is the object of thepreliminary drying to prevent the photomask from adhesion tointerlaminar insulating layer at the time of irradiation with activeenergy beam. By irradiating an active energy beam through a photomask,the photosensitive acid generator is activated and the imidazolecompound is inactivated. Subsequently, the heat curing step (I) ispracticed to cure the unexposed area. Then, the exposed area isdissolved and eliminated with a developer, for instance an organicsolvent, the residue is rinsed, and then the heat curing step (II) ispracticed to form a via-carrying insulating layer. Preferable conditionof the heat curing step (I) is 95–120° C. for 30–120 minutes, andpreferable condition of the heat curing step (II) is 130–200° C. for30–480 minutes. In the multilayered circuit board of buildup mode usingthe composition of the present invention, a plurality of interlaminarinsulating layers are formed in succession, due to which the layers aredifferent from one another in heat history. For the purpose of lesseningthe differences in heat resistance, flexibility and adhesive propertybetween the layers due to the difference in heat history, the heatcuring step (II) may be divided into two sub-steps. For example, all thelayers are heat-cured and formed at 150° C. for 60 minutes, andthereafter all the layers are heat-cured at 180° C. for 240 minutes. Theterm “cure” herein used means a process of transformation during which acomposition of the present invention which is originally soluble in asuitable solvent or fusible upon heating is transformed into aninsoluble and infusible 3-dimensional crosslinked product through aprocess of heating.

In the next step, resin surface of interlaminar insulating layer andinner wall of via holes are subjected to a roughening treatment for thepurpose of removing the scum from the bottom of via holes and improvingthe adhesion between copper plating layer and interlaminar insulatinglayer in the subsequent plating step. As the method for the rougheningtreatment, mechanical grinding methods such as buffing, sand blasting,jet scrubbing, etc.; plasma etching treatment; and chemical treatmentsusing an oxidant such as potassium permanganate, sodium permanganate,potassium bichromate, ozone, hydrochloric acid, nitric acid, sulfuricacid-hydrofluoric acid, etc. can be used. In carrying out the rougheningtreatment of interlaminar insulating layer using an oxidant, the surfaceof the interlaminar insulating layer is preferably swollen with anorganic solvent such as N-methyl-2-pyrrolidone, N,N-dimethylformamide,dimethylacetamide, dimethyl sulfoxide, methoxypropanol, -butyrolactoneor the like prior to the treatment. Subsequently, a conductor layer isformed by electroless plating and/or electrolytic plating. Thickness ofthe electroless plating layer is 0.2 to 3 μm, and thickness of theelectrolytic plating layer is 5 to 30 μm. After formation of theconductor layer, an annealing treatment is carried out at 130–200° C.for 10 to 60 minutes for the purpose of stabilizing the plating layer. Aconductor circuit can be formed according to known method. For example,a photosensitive etching resist is applied onto the plating layer, theresist is exposed to light through a mask having a circuit pattern, andthen development is carried out to form a pattern. The copper in theopening part of etching resist formed by development is etched with anacid to form a copper pattern. Then, the etching resist is peeled off toform a conductor circuit. Alternatively, after applying an electrolessplating catalyst onto the interlaminar insulating layer, a platingresist having a pattern inverse to that of conductor layer is formed. Ifdesired, a conductor circuit may be formed by electroless plating only.

By repeating the above-mentioned procedure several times, a multilayeredprinted circuit board in which a plurality of buildup layers arelaminated can be obtained.

As the inner layer circuit substrate onto which the positive typephotosensitive epoxy resin composition of the present invention iscoated, epoxy substrate, polyester substrate, polyimide substrate, BTresin substrate, ceramic substrate, thermosetting PPE substrate and thelike can be used. Although these inner layer circuit substrates may bemade of a brominated resin, they are preferably made of non-brominatedresin having a flame-retarding construction. As the reinforcingmaterial, glass fiber, aramide fiber and the like are preferable. Thesurface of conductor is preferably subjected to a roughening treatmentpreviously in order to improve the adhesion between the conductorsurface and interlaminar insulating layer. As the method of roughening,a method of forming needle-like crystals on the conductor surface by anoxidation treatment (blackening treatment) and thereafter subjecting theexcessively grown needle-like crystals to a reductive treatment, amethod of micro-etching using a mixed solution of an organic acid and acupric complex compound, a method of needle-like alloy plating usingcopper/nickel/phosphorus system, etc. can be referred to.

The irradiation of the positive type photosensitive resin composition ofthe present invention, namely the step of exposure, is preferablycarried out by using radiation of a wavelength of 250 to 600 nm, and thequantity of energy is preferably 150 to 8,000 W. The light source whichcan be used are, for example, xenon lamp, argon lamp, tungsten lamp,carbon arc, metal halide and metal arc lamp (low pressure, mediumpressure, high pressure and ultra-high pressure mercury lamps) orsuitable lasers. Preferably, metal halide and metal arc lamp are used.After the irradiation, the composition is heat-cured by means of usualhot air circulating furnace. When a short time period of heating or ashort time period of reaction is required, IR-irradiation, IR-laser ormicrowave apparatus may be used, if desired.

For coating the composition of the present invention, known methods suchas spin coater method, roll coater method, screen coater method, diecoater method, curtain coater method, spray coater method and the likecan be used. The coating may be carried out multiple times for thepurpose of obtaining a desired thickness of interlaminar insulatinglayer. In accordance with object which may be sometimes to smooth thesurface or sometimes to fill up the via holes, other coating methods maybe combined with the above-mentioned coating methods, and the coatingmay be carried out multiple times.

Examples of the solvents which can be used at the time of developmentinclude organic solvents like ketones such as methyl ethyl ketone,methyl isobutyl ketone, cyclohexanone and the like; cellosolves such ascellosolve, butyl cellosolve and the like; carbitols such as methylcarbitol, dimethyl carbitol, butyl carbitol and the like; carboxylicesters such as ethyl acetate, butyl acetate, cellosolve acetate, butylcellosolve acetate, methoxypropyl acetate, carbitol acetate, butylcarbitol acetate, propylene carbonate, -butyrolactone and the like;alcohols such as butanol, methoxypropanol and the like;N-methyl-2-pyrrolidone, N,N-dimethylformamide, and dimethylacetamide, orusual aqueous alkaline developers. Mixtures of two ore more of thesesolvents are also usable.

The solvents which can be used for the rinsing include water; alcoholssuch as ethanol, isopropanol and the like; hydrocarbons such as hexane,cyclohexane and the like; and aromatics such as toluene, xylene and thelike.

EXAMPLES

Next, the present invention is explained in more detail by referring toexamples. The invention is by no means limited by these examples.

Table 1 illustrates details of the epoxy resin, triazine ring-containingmodified phenolic resin, imidazole compound and photosensitive acidgenerator used in the Examples and the phenolic resin used in theComparative Examples.

Table 2 illustrates Examples, and Table 3 illustrates ComparativeExamples.

After preliminarily mixing the ingredients of Fluid A shown in Tables 2and 3, the mixture was kneaded by means of wet beads mill and filteredby means of a 10 μm filter. The ingredients of Fluid B were heated toform a solution and then filtered by means of a 10 μm filter. Then,Fluid A and Fluid B were mixed together and used for the tests ofExamples and Comparative Examples.

1) Heat Resistance Test

A mixture of Fluid A and Fluid B was coated by means of a curtain coateronto a non-brominated flame-retardant epoxy/glass substrate carrying aconductor circuit of 0.8 mm thick which had been subjected to ablackening-reduction treatment, so as to give a dry coating thickness,on conductor, of 30 μm. After drying the coat at 25° C. for 15 minutesunder an air stream, the dried coat was further dried in a hot aircirculating furnace at 80° C. for 15 minutes. After cooling the coatedsubstrate, backside of the substrate was coated so as to give a drycoating thickness, on conductor, of 30 μm, dried under an air stream at25° C. for 15 minutes and then dried in a hot air circulating furnace at80° C. for 30 minutes. Then, ultraviolet ray having a wavelength of 365nm was irradiated through a photomask at a dosage of 1,000 mJ/cm², afterwhich the heat-curing step (I) was carried out at 105° C. for 60minutes. After cooling the test piece to ambient temperature, (I) wascarried out, -butyrolactone was sprayed for 1.5 minutes and then waterwas sprayed for 20 seconds. After development and rinsing, theheat-curing step (II) was carried out first at 150° C. for 60 minutesand then at 180° C. for 120° C.

The test piece was dipped in a solder bath at 260° C. for 10 secondsaccording to the testing method of JIS C6481, and then the test piecewas examined for swelling and cracking.

-   -   A: No change at all    -   B: A slight change noticeable    -   C: A marked change noticeable    -   D: Swelling and cracking noticeable in the interlaminar        insulating layer        2) Resolution

Each of the compositions of Examples and Comparative Examples was coatedonto a blackened and reduced substrate by means of a curtain coater soas to give a dry coating thickness of 50 μm, dried under an air streamat 25° C. for 15 minutes, and then dried in a hot air circulatingfurnace at 80° C. for 30 minutes. After cooling the coated matter toambient temperature, ultraviolet ray having a wavelength of 365 nm wasirradiated through a photomask at a dosage of 1,000 mJ/cm², and then theheat curing step (I) was carried out at 105° C. for 60 minutes. Aftercooling the test piece to ambient temperature, -butyrolactone wassprayed for 1.5 minutes and then water was sprayed for 20 seconds, afterwhich development and rinsing were carried out. Then, the heat-curingstep (II) was carried out first at 150° C. for 60 minutes and thereafterat 80° C. for 120 minutes to cure the test piece. Then, via holeformability at the opening part of photomask having a diameter of 70 μmwas examined.

-   -   A: Via hole having a diameter of 70 μm was formed, and        development reached the bottom of via hole.    -   B: Via hole having a diameter of 70–100 μm was formed, and        development reached the bottom of via hole.    -   C1: Via hole having a diameter of 40 μm or less was formed, and        development did not reach the bottom of via hole.    -   C2: Via hole having a diameter of 100 μm or above was formed,        and the surface was tacky after development.    -   D1: The exposed area also cured, and no via hole was formed.    -   D2: After development, the unexposed area was also found to be        developed.        3) Flame Retardance Test

Copper was etched off from both sides of a non-brominatedflame-retardant epoxy/glass substrate having a thickness of 0.8 mm. Thenthe substrate was coated so as to give a dry coating thickness of 40 μm,and dried under an air stream at 25° C. for 15 minutes and then in a hotair circulating furnace at 80° C. for 15 minutes. After cooling the testpiece to ambient temperature, the backside was coated so as to give adry coating thickness of 40 μm, and dried under an air stream at 25° C.for 15 minutes and then in an hot air circulating furnace at 80° C. for30 minutes. The above-mentioned procedure was again repeated, as aresult of which the total thickness of dry coatings on one side came to80 μm. Then, the heat-curing step (I) was carried out at 105° C. for 60minutes, and thereafter the heat-curing step (II) was carried out firstat 150° C. for 60 minutes and then at 180° C. for 120 minutes to curethe test piece.

Flammability of the test piece was examined and judged according to thedescription of Underwiters Laboratories: “Test for Flammability ofPlastic Materials, UL-94”.

4) Processability

A cold-rolled steel plate having a thickness of 0.8 mm which had beendefatted with cyclohexanone and acetone was coated by means of a barcoater so as to give a dry coating thickness of 30 μm, dried under anair stream at 25° C. for 15 minutes, and then dried in a hot aircirculating furnace at 80° C. for 30 minutes. Then, the heat-curing step(I) was carried out at 105° C. for 60 minutes, and the whole area wasirradiated with an ultraviolet ray having a wavelength of 365 nm at adosage of 1,500 mJ/cm². Then, the heat-curing step (II) was carried outfirst at 150° C. for 60 minutes and thereafter at 180° C. for 120minutes to cure the test piece. Elongation of the test piece wasmeasured by means of Erichsen tester.

[Effect of the Invention]

According to the method of the present invention, a multlayered printedcircuit board of buildup mode superior in resolution, heat resistance,flexibility and electrical insulating property and capable of exhibitinga flame retardance without using any of brominated resin and antimonycompound can be obtained in a high productivity.

TABLE 1 Epoxy resin A Liquid Bisphenol A type epoxy resin Epoxy eq. =189 g/mol, viscosity = 13,000 mPa · s (25° C.), Total chlorine content =1,200 ppm Epoxy resin B Bisphenol A type epoxy resin Epoxy eq. = 460g/mol, Softening point = 68° C., Total chlorine content = 1,200 ppmEpoxy resin C Bisphenol A type epoxy resin Epoxy eq. = 760 g/mol,Softening point = 94° C., Total chlorine content = 1,100 ppm Epoxy resinD Oxazolidone ring-containing Bisphenol A type epoxy resin Epoxy eq. =340 g/mol, Softening pt. = 78° C., Total chlorine content = 1,000 ppm,Oxazolidone ring content eq. = 630 g/mol Epoxy resin F Phenol novolactype epoxy resin Epoxy eq. = 178 g/mol, Viscosity = 45,000 mPa · s (52°C.), Total chlorine content = 1,600 ppm Triazine ring-containingFormaldehyde/phenol/ modified phenolic resin benzoguanamine Hydroxyl eq.= 230 g/mol, Softening pt. = 105° C., Nitrogen content = 20% Phenolicresin Formaldehyde/phenol Hydroxyl eq. = 105 g/mol, Softening pt. = 98°C. Imidazole compound A 2-Ethyl-4-methylimidazole Imidazole compound B2-Phenylimidazole Iron allene complex compound A (η⁶-Cumene)(η⁵-cyclopentadiene) Fe-hexafluorophosphate Iron allene complex compoundB (η⁶-Cumene) (η⁵-cyclopentadiene) Fe-trifluoromethylsulfonate

TABLE 2 Ex. 1 Ex. 2 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Fluid A Epoxy rosin A 5.45.4 Epoxy resin B 10.8 10.8 Epoxy resin C 43.5 43.5 43.5 43.5 Epoxyresin D 37.9 37.9 Epoxy resin E 10.9 10.9 10.9 10.9Methylmercaptotetrazole 0.1 0.1 0.1 0.1 0.1 0.1 Polyether-modified 0.20.2 0.2 0.2 0.2 0.2 dimethylsiloxane Polymethylalkylsiloxane 0.2 0.2 0.20.2 0.2 0.2 Aerosil R-972 1.7 1.7 1.7 1.7 1.7 1.7 Magnesium hydroxide12.0 12.0 12.0 12.0 Iron allene complex 1.1 1.1 1.1 compound A Ironallene complex 1.2 2.0 2.0 compound B Diethylthioxanthone 0.5 0.5 0.50.5 0.5 0.5 Methoxypropyl acetate 42.0 42.0 42.0 42.0 42.0 42.0 Fluid BPhenolic resin Triazine ring-containing 12.9 12.9 12.9 12.9 17.9 17.9modified phenolic resin Imidazole compound A 0.3 Imidazole compound B0.4 0.4 0.4 0.6 0.6 Methoxypropyl acetate 16.0 16.0 16.0 16.0 16.0 16.0Heat resistance A A A A A A Resolution B B A B B A Flame retardance V-1V-1 V-1 V-1 V-0 V-1 Flexibility (mm) 6 6 6 6 7 7Methylmercaptotetrazole: Adhesion improver Polyether-modifiedpolydimethylsiloxane: Leveling agent Polymethylalkylsiloxane:Antifoaming agent Aerosil R-972: Thixotropic agent Magnesium hydroxide:Inorganic filler

TABLE 3 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.5 Ex. 6 Fluid A Epoxy resin A Epoxy resin B Epoxy resin C 43.5 43.5 43.543.5 43.5 43.5 Epoxy resin D Epoxy resin E 10.9 10.9 10.9 10.9 10.9 10.9Methylmercaptotetrazole 0.1 0.1 0.1  0.1 0.1 0.1 Polyether-modifieddimethylsiloxane 0.2 0.2 0.2  0.2 0.2 0.2 Polymethylalkylsiloxane 0.20.2 0.2  0.2 0.2 0.2 Aerosil R-972 1.7 1.7 1.7  1.7 1.7 1.7 Magnesiumhydroxide 12.0 12.0 12.0 12.0 12.0 12.0 Iron allene complex compound A1.1 1.1 1.1  1.1 0.1 2.3 Iron allene complex compound BDiethylthioxanthone 0.5 0.5 0.5  0.5 0.5 0.5 Methoxypropyl acetate 42.042.0 42.0 42.0 42.0 42.0 Fluid B Phenolic resin 10.6 Triazinering-containing 12.9 12.9 12.9 12.9 modified phenolic resin Imidazolecompound A Imidazole compound B 0.4 0.4 0.1  2.6 0.4 0.4 Methoxypropylacetate 16.0 16.0 16.0 16.0 16.0 16.0 Heat resistance A A B D B CResolution B B D2 D1 C1 C2 Flame retardance Flam. Flam. V-1 V-1 V-1 V-1Flexibility (mm) 6 2 4  1> 6 2 Com. Ex. = Comparative Example Flam. =Flammable Methylmercaptotetrazole: Adhesion improver Polysther-modifiedpolydimethylsiloxane: Leveling agent Polymethylalkylsiloxane:Antifoaming agent Aerosil R-972: Thixotropic agent Magnesium hydroxide:Inorganic filler

1. A positive type photosensitive epoxy resin composition comprising (a)an epoxy resin having two or more epoxy groups in one molecule; (b) amodified phenolic resin having a triazine ring, (c) a latent basiccuring agent, and (d) a photosensitive acid generator.
 2. The positivetype photosensitive epoxy resin composition claimed in claim 1, whereinthe latent basic curing agent is an imidazole compound.
 3. The positivetype photosensitive epoxy resin composition claimed in claim 1, wherein10 to 90% by weight of said epoxy resin is occupied by a Bisphenol Atype epoxy resin having an epoxy equivalent of 400 to 1,000 g/mol and asoftening point of 40 to 100° C.
 4. The positive type photosensitiveepoxy resin composition claimed in claim 1, wherein 2 to 15% by weightof said epoxy resin is occupied by a Bisphenol A type epoxy resin havingan epoxy equivalent of 175 to 210 g/mol and being in a liquid state atnormal temperature.
 5. The positive type photosensitive epoxy resincomposition claimed in claim 1, wherein 5 to 20% by weight of said epoxyresin is occupied by a novolac type epoxy resin having an epoxyequivalent of 175 to 230 g/mol.
 6. The positive type photosensitiveepoxy resin composition claimed in claim 1, wherein 20 to 80% by weightof said epoxy resin is occupied by an epoxy resin having an oxazolidonering in the molecule thereof which is a reaction product between anepoxy resin and a diisocyanate.
 7. The positive type photosensitiveepoxy resin composition claimed in claim 6, wherein said epoxy resinhaving an oxazolidone ring in the molecule thereof has an epoxyequivalent of 230 to 500 g/mol, an oxazolidone ring equivalent of 400 to1,300 g/mol and a softening point of 50° C. to 120° C.
 8. The positivetype photosensitive epoxy resin composition claimed in claim 1, whereinsaid modified phenolic resin having a triazine ring is a condensate of aphenol compound, a compound having a triazine ring and an aldehyde. 9.The positive type photosensitive epoxy resin composition claimed inclaim 1, wherein said modified phenolic resin having a triazine ring hasa phenolic hydroxy equivalent of 120 to 300 g/mol, a softening point of80° C. to 150° C. and a nitrogen content of 4 to 25% by weight.
 10. Thepositive type photosensitive epoxy resin composition claimed in claim 9,wherein said modified phenolic resin having a triazine ring has aphenolic hydroxy equivalent of 150 to 250 g/mol, a softening point of90° C. to 140° C. and a nitrogen content of 15 to 25% by weight.
 11. Thepositive type photosensitive epoxy resin composition claimed in claim 1,wherein 0.2 to 0.8 equivalents of phenolic hydroxyl group of themodified phenolic resin is compounded with one equivalent of epoxy groupof the epoxy resin.
 12. The positive type photosensitive epoxy resincomposition claimed in claim 11, wherein 0.2 to 0.5 equivalents ofphenolic hydroxyl group of the modified phenolic resin is compoundedwith one equivalent of epoxy group of the epoxy resin.
 13. The positivetype photosensitive epoxy resin composition claimed in claim 1, whereinthe latent basic curing agent is an epoxy adduct wherein 0.01 to 0.10equivalent of an imidazole compound is compounded with one equivalent ofepoxy group of an epoxy resin.
 14. The positive type photosensitiveepoxy resin composition claimed in claim 13, wherein 0.015 to 0.04equivalent of an imidazole compound is compounded with one equivalent ofepoxy group of an epoxy resin.
 15. The positive type photosensitiveepoxy resin composition claimed in claim 1, wherein said photosensitiveacid generator is an iron arene complex compound represented by thefollowing formula:[R¹(Fe^(II)R²)]⁺[X]⁻ wherein R¹ is a π-arene and R² is a π-arene or aπ-arene anion and X is a non-nucleophilic anion.
 16. The positive typephotosensitive epoxy resin composition claimed in claim 1, whereinequivalent ratio of said photosensitive acid generator is 0.2 to 1.4equivalents per equivalent of the latent basic curing agent.
 17. Thepositive type photosensitive epoxy resin composition claimed in claim16, wherein equivalent ratio of said photosensitive acid generator is0.40 to 95 equivalents per equivalent of the imidazole compound.
 18. Amethod for forming an insulating layer characterized by coating asubstrate with a positive type photosensitive epoxy resin compositioncomprising (a) an epoxy resin having two or more epoxy groups in onemolecule; (b) a modified phenolic resin having a triazine ring, (c) alatent basic curing agent, and (d) a photosensitive acid generator,followed by the step of preliminary drying at a temperature not higherthan the temperature at which the subsequent heat curing step (I) is tobe carried out, a step of imagewise irradiating the coating with anactive energy beam, a heat curing step (I), a step of dissolving andeliminating the exposed area, and an additional heat curing step (II).19. The method claimed in claim 18, wherein the latent basic curingagent is an imidazole compound.
 20. The method for forming an insulatinglayer claimed in claims 18 or 19, wherein the temperature of the heatcuring step (I) is 95° C. to 120° C., and the temperature of the heatcuring step (II) is 130° C. to 200° C.
 21. The method claimed in claims18 or 19, wherein the dissolving and eliminating of the exposed area iscarried out with an organic solvent.
 22. The method claimed in claims 18or 19, wherein the insulating layer is an interlaminar layer.